1. Field of the Invention
The present invention relates to an electromagnetic shield for preventing leakage of electromagnetism to the outside from a high-frequency oscillation circuit placed in electronic equipment such as a portable telephone. More particularly, the invention pertains to an electromagnetic shield structure that establishes electric connections between electromagnetically shielding areas on front and rear cases of an electronic equipment housing.
2. Description of the Prior Art
In FIGS. 12 through 14 there is depicted a prior art example (Japanese Patent Application Laid-Open No. 46396/97), in which the housing of a portable telephone is made up of a rear case (a main body) 1 and a front case (a cover) 3. In the rear case 1 there is disposed a printed-circuit board 6, on which a high-frequency oscillation circuit 7 and other electronic parts are mounted.
The interior surfaces 9 of the front and rear cases 3 and 1 and the surfaces of partition walls 11 formed integrally with the rear case 1, surrounding the high-frequency oscillation circuit 7, are each coated with a metal shield layer (not shown), for example, by nickel plating or copper evaporation.
On each partition wall 11 coated with the metal shield layer, there is mounted a metal contact piece 13 in straddle fashion as shown in FIG. 13. The contact piece 13 has an inverted U-shaped cross-section in its entirety and has a gripping portion 15, which grippingly engages the top of the partition wall 11 and hence is electrically connected to the metal shield layer coated all over it,
Reference numeral 17 denotes resilient contact portions cut and raised obliquely upward from the contact piece 13.
On the printed-circuit board 5 disposed in the rear case 1 there are printed at places opposite the contact portions 17 grounding patterns 19 serving as shielding areas. When the front and rear cases 3 and 1 are assembled into the telephone housing, the contact portions 17 are pressed into resilient contact with the grounding patterns 19. This resilient contact establishes electrical connections between the metal shield layer of the front case 1 and the shielding areas of the rear case 3, i.e. the grounding patterns 19 on the printed-circuit board 5, provide an electromagnetic shielding around the high-frequency oscillation circuit 7.
In FIG. 16 there is depicted another prior art example, in which a contact piece 21 has a flat, U-shaped cross-section and its opposed tip end portions form resilient contact portions 23. The contact piece 21 is soldered to a grounding pattern 29 on a printed-circuit board 27 placed in a rear case 25. The contact portions 23 make resilient contact with a partition wall 33 of a front case 31. In this instance, the contact portions 23 contact the ceiling 37 of a recess 36 made in the partition wall 33.
The contact pieces 13 and 21 of the both prior art examples are each obtained by punching a sheet of phosphor bronze into a blank of a predetermined shape and bending it at right angles or obliquely to its surface. These contact pieces 13 and 21 are both so small that their bending inevitably involves precision machining, resulting in an increase in the manufacturing costs of electronic equipment.
Further, the gripping engagement of the gripping portion 16 of each contact piece 13 with the top of the partition wall 11 requires the formation of the wall 11 to a height large enough to provide for the height H of the gripping portion 15 as shown in FIG. 14. This makes it difficult to reduce the thickness of the entire housing structure by decreasing the height of the partition wall 11.
In the prior art example of FIG. 16, soldering of the contact piece 21 to the grounding pattern 29 requires that the latter to be formed over a wide area--this inevitably lowers the packaging density of other electronic parts over the entire area of the printed-circuit board 27.